Device for polishing workpiece surfaces

ABSTRACT

A device for polishing metallic workpiece surfaces. The device includes a tool holder which can be exchangeably fitted into a rotationally driven working spindle of a program-controlled milling machine, and a polishing tool, which is fastened in the tool holder. The device also includes a tool shank and a polishing head at the free end thereof, and is coupled to a polishing agent supply, which arrives at the effective surface of the polishing head. The tool shank contains a chamber, which can admit a pressure medium and is at least partially filled with the polishing agent, wherein this chamber is in connection with the polishing head by way of a channel and wherein the polishing head has polishing agent permeable material or it contains passages for the polishing agent that is forced out of the chamber.

The invention relates to an apparatus for polishing preferably metallic workpiece surfaces, comprising a polishing tool which can be moved in several axes and has a polishing head attached thereto.

Although a plurality of polishing machines having fine grinding and/or polishing tools for polishing the most differing workpieces is known, the machined surfaces of structures produced in machining centers and program-controlled milling machines have been high-gloss polished by hand to date. When the structures have large volumes for presses, the polishing work to be carried out manually is extremely time-consuming. Furthermore, since the structures often have complex surfaces including roundings, edges and curvatures, automated polishing of the entire surfaces including their critical areas was formerly not possible by means of the program-controlled milling machine. The polishing of pressed and cast parts which, to obtain high gloss, is usually to be carried out in several steps by hand or also by means of power tools, is extremely time-consuming and calls for highly qualified, experienced staff.

In order to polish simply curved glass surfaces in the production of optical lenses, it is known from DE 103 14 625 B3 to remove material in well-calculated fashion on the workpiece surface by fine grinding or polishing using a rotationally driven polishing tool. The polishing tool contains a tool shank which is fixed in a spindle of a special polishing machine or a robot by means of a tool holder. A hollow-cylindrical head is mounted on the tool shank, and a cylindrical polishing member is received in a longitudinally movable fashion in the outwardly open chamber of said head. A polishing suspension impinges on the inner rear side of the polishing member which is moved in rotating and oscillating fashion and forces the polishing member with its annular and cylindrical polishing surface against the curved surface of the glass workpiece. The polishing suspension passes through an annular gap between the polishing element and the chamber wall and reaches the glass surface to be polished. This apparatus cannot be used in program-controlled milling machines and machining centers and cannot process the curvatures which are often narrow in the case of pressed parts with the required accuracy.

In addition, as method and an apparatus for the production of structures is known from DE 10 2006 017 664 A1, wherein a three-dimensional structure is milled out of a material block by means of a processing machine and then the structure surface is smoothed in several processing operations by fine grinding and polishing using the work spindle movable in five axes. The tools used for polishing have an approximately spherical head which is attached to the free end of a longitudinally movable pin. The polishing head consists of a suitable material deformable within limits, e.g. is made of felt, fabric fibers, plastic material, etc. The polishing head is pressed on the structure surface of the respective workpiece, which is to be smoothed, at a predetermined contact pressure by means of an installed spring element, wherein the quantity of the contact pressure can be adjusted via the machine control. However, these polishing operations create problems with respect to effective supply of the polishing agent to the surface area to be processed.

The object of the invention is to create a system for the automated polishing of in particular machined workpiece surfaces by means of a program-controlled milling machine, wherein the system can be integrated into the operating sequences of the milling machine and guarantees an optimization of the polishing operations and a controlled supply of the polishing agent to the processed surface area.

In order to achieve the above-mentioned object, the subject matter of the invention is an apparatus for polishing machined workplaces, comprising a polishing tool which can be exchangeably fitted into the work spindle of the processing machine and has a polishing head arranged on the and side thereof, wherein the tool shank of the polishing tool contains a pressurized chamber which is at least partially filled with a polishing agent and is connected to the polishing head, wherein said polishing head has passages for the polishing agent forced out of the chamber. The multi-part polishing tool which is movable via the work spindle of the machine tool in several axes, in particular in five axes, contains a shank and a polishing head attached to the free end thereof. The tool shank can be mounted on a tool holder, e.g. what is called a machine taper, which is clamped as usual in the work spindle of the CNC-controlled milling machine. The polishing head which is rotationally driven in predetermined speed ranges of several 1000 rpm via the work spindle preferably consists of a wear-resistant deformable material and is moved over the workpiece surface to be processed at a virtually constant slight contact pressure by means of the work spindle.

An essential aspect of the invention is that the polishing tool or also a series of different polishing tools is integrated into the functional system of a program-controlled milling machine operating preferably in five axes, and therefore the workpiece can be polished, optionally in several stages, with equal clamping and without temporal interruption when the grinding and/or smoothening operations have been concluded. The operating system according to the invention allows for the possibility of having several polishing tools with the respective tool holders available in a correspondingly designed tool magazine and of exchangeably fitting them into, or remove them from, the work spindle as usual and as required using the machine-specific tool changer. Since the polishing work, e.g. consisting of prepolishing and high gloss polishing, takes considerable time, it is recommended to polish relatively large workpieces during the night shift.

In an advantageous exemplary embodiment of the invention, a pressure medium channel communicating with the pressure medium supply of the machine tool is formed in the tool shank, said channel extending either to the shank end or to a chamber in the shank, said chamber forming a piston-cylinder unit. A pressure medium of the machine tool impinges on the piston of this piston-cylinder unit via the longitudinal channel and the piston is pressed against a polishing agent filling with which the cylinder chamber is filled. The more or less viscous polishing agent is forced via the terminally discharging bores in the tool shank into the polishing head by means of the pressure exerted on the piston which is longitudinally slidable in the chamber. The polishing head is thus supplied with the polishing agent. In order for the polishing agent to reach the outer surface of the polishing head in sufficient and adjustable amount, the polishing head has passages for the polishing agent. For this purpose, the polishing head can have a suitable porosity or fine through-holes. The polishing agent is uniformly distributed over the head surface by means of the centrifugal forces which are effective while the polishing head rotates.

In a variant of the apparatus according to the invention, which is particularly useful in practice, the piston-cylinder unit is made as an exchangeable cartridge which can be inserted in the chamber of the tool shank. This cartridge preferably consists of a suitable—cost-effective—plastic material and its cylinder chamber below the piston is filled with a predetermined amount of polishing agent. The polishing agent can have a viscosity and grain size which are selected specifically for the particular polishing process to be carried out.

The tool shank can preferably consist of several individual parts, e.g. of a machine-side clamping part which has fixing and clamping members for the fixed installation in a tool holder and of a shank part containing the piston-cylinder unit and the polishing head. The outer shank part of this polishing tool can be exchangeable and can have different diameters and lengths, for example, so as to be able to carry out diverse polishing operations. Having detached the connecting members to the machine-side clamping part, the external shank part can be disassembled and the cartridge can be exchanged with a new cartridge having the same or another polishing agent.

An optimized adaptation to different workpiece materials and structures can be achieved according to another useful development of the invention by producing the polishing head from suitable fiber-composite materials. By means of a detachable connection of the polishing head to the external shank part, it is possible to exchange e.g. worn polishing heads rapidly and easily. Composite materials have proved to be particularly suitable materials with respect to the effect of removal and to wear: they consist of an elastically deformable inner body and a fabric which is attached to the surface thereof in fixedly adhering manner and is made of synthetic fibers which have an extreme loadability, tensile strength and temperature resistance and are available e.g. as a PBO fabric under the trade name of “Zylon”. The inner rubber holding body of the polishing head can be provided with one or several layers of this PBO fabric. The arrangement of a first layer made of a felted fiber material and, on top thereof, of a coarse-meshed PBO fabric as a wear protection is also possible in practice.

In the program-controlled milling machines and machining centers in which the apparatus according to the invention is inserted, the KS media, such as an internal cooling lubricant, an external cooling lubricant and outer blow air, are blocked during the polishing operation. What is used is only the blow air through the spindle center of the work spindle, which exerts the necessary pressure on the piston in the piston-cylinder unit and thus also on the polishing agent. This internal blow air is regulated by a pressure control valve, which is driven by the machine control so as to regulate the polishing agent amount forced out of the chamber towards the polishing heads. This polishing amount supplied to the effective surface of the polishing head can be adjusted or varied via the pressure of the blow air in the work spindle or also by means of an adjustment nozzle depending on the polishing tasks, the materials to be processed, the composition of the polishing agent and also other parameters of the polishing process, e.g. the contact pressure of the polishing head on the workpiece, wherein the adjustment nozzle is arranged in the channel section of the outer shank part between the cylinder chamber and the polishing head.

Exemplary embodiments of the invention are described in detail below by means of the drawing, wherein

FIG. 1 shows a partially cut side view of the front part of a milling spindle, a tool holder and a polishing tool design;

FIG. 2 shows an axial section of a polishing tool without tool holder;

FIG. 2 a shows an axial section of the front part of the polishing tool according to FIG. 2 having a modified polishing head;

FIGS. 3, 4 show a partially cut side view of polishing tools clamped in different tool holders;

FIG. 5 shows a diagram of the inner blow air control of the work spindle with a pressure control valve.

FIG. 1 shows an axial partial section of the end portion of a work spindle 1 of a milling machine—not shown—which is program-controlled in five axes, for example, wherein this work spindle 1 is made as what is called a motor spindle. In this work spindle 1, a hydraulically clampable mount 2 is accommodated in axially slidable fashion in its central through-hole, and a tool holder 4 can be fixed in detachable fashion via suitable inner clamping elements in the work spindle 1 by means of this mount. The work spindle 1 also contains central flow channels for cooling lubricant and compressed air. These fluids are sprayed onto the processed workplace surface during the milling operation by the milling cutter. The machine holder 4 shown in FIG. 1 corresponds to the design WZ_HSK63 of FIG. 4. Correspondingly, it is possible to use a steep taper tool holder WZ_SK40 shown in FIG. 3 instead of this tool holder 4—when the work spindle 1 is designed correspondingly. Both tool holders can automatically be exchangeably fitted into and removed from the work spindle by means of a common tool changer.

The drawing shows a polishing tool 10 as an exemplary embodiment of the invention, said polishing tool having a tool shank 15 composed of two parts 11, 12 via a sleeve 13. Both shank parts 11, 12 have a cylindrical outer shape and consist of metal or of a sufficiently rigid and dimensionally stable plastic material to obtain a sufficient flexural rigidity. An approximately semi-spherical polishing head 16 is attached to the free end of the outer shank part 11 and can have an outer diameter which is slightly larger than that of the outer shank part 11.

The polishing head 16 consists of a suitable material, e.g. of hardened felt, of a sponge-like or brush-like material, an elastomer which can be shaped within certain limits, a fiber composite material or the like. In practice, a polishing head has proved particularly successful that has an inner body made of a rubber or elastomer of predetermined hardness, on the surface area of which a fabric made of high-strength synthetic fibers, e.g. of a PBO fabric, is fixed. These fibers are available under the trade name of “Zylon”.

FIGS. 2 and 2 a show two possible embodiments of polishing heads 16 in a schematic axial section. As shown, each polishing head 16 has a rounded shape or the shape of a spherical segment and can be fixed at the free end portion of the shank part 11 in detachable fashion or also permanently, e.g. by adhering or vulcanization. What is feasible is also a milling head having a rotary wire brush, the wires of which extend parallel to the axis of rotation of the wire brush and are oriented approximately perpendicularly to the workplace surface.

The tool shank 15 of the polishing tool 10 according to the invention can have several parts or also one part, wherein a liquid or pasty polishing agent, which is required for polishing and has a suitable viscosity, is applied continuously or intermittently to the outer surface of the polishing head 16. The multi-part tool shank 15 has a machine-side inner shank part 12 in which a central longitudinal channel 18 is formed. This longitudinal channel 18 is connected to the compressed air system of the milling machine and/or the work spindle thereof. In the polishing operation, the compressed air is supplied via a pressure control shown in FIG. 5 by way of diagram. A pressure control valve 38 regulates the supply of the inner blow air to the work spindle 1. The supply of other operating material, such as cooling lubricant, to the work spindle 1 or to the polishing tool 10 is blocked during the polishing operation.

As also evident from FIG. 2, a locating notch 19 is formed in the inner shank part 12 for rotary protection, and a countersunk screw 20 screwed into the tool holder 4 is immersed into said notch (see FIG. 4). In the outer shank part 11 which is on the left-hand side in FIG. 2, a cylindrical chamber 22 is made as a recess which is open on the right-hand side and extends over a conical end portion 23 to a bore 24 of reduced diameter. Downstream of this bore 24, a cock-like control waive 26 is disposed in an axial channel 25. The channel 25 ends in a funnel-like pressure chamber 27 surrounded by the polishing head 16, and several through-holes 28 in the polishing head 16 extend from said chamber to the outer side thereof. These bores 28 form passages for a polishing agent forced out of the chamber 22 by pressurizing the piston 31 provided in this chamber 22 in longitudinally slidable fashion. The chamber 22 can be filled directly with a liquid or pasty polishing agent which is forced to the polishing head 16 by the application of an external pressure to the displacement piston 31 longitudinally slidable in the chamber 22.

In the polishing tool 10 according to FIG. 2, the piston 31 is slidably arranged in an axial direction in the interior of the elongated cylindrical chamber 22 in the outer shank portion 11, and the inner blow air of the work spindle impinges on the front side thereof which is shown on the right in FIG. 2 and which is pressed against a polishing agent filling in the left-hand portion of the chamber. In this embodiment, the shank part 11 must be separated from the machine-side shank part 12 by loosening the cap nut 13 when the polishing agent is depleted and the chamber 22 has to be refilled; the same applies when another polishing head 16 shall be inserted.

An advantageous variant can be taken from FIG. 2. In this embodiment, an inexpensive cartridge 30 made of a plastic material, for example, is inserted in the hollow-cylindrical shank part 11, i.e. in the cylindrical chamber 22, where the piston 31 is guided in axially slidable fashion. This cartridge 30 extends over the entire length of the cylindrical chamber 22 up into a deep annular groove in the widened end portion of the shank part 12 on the right-hand side in FIG. 2. The chamber 32 of the cartridge 30, which is on the left-hand side in FIG. 2, is filled with a suitable polishing agent. Compressed air is introduced via the central longitudinal channel 18 into the pressure chamber 33 on the right-hand side of the piston 31 either continuously or in the form of time-controlled pressure surges so as to exert on the piston 31 compressive forces directed to the left. The cartridge 30 is held in positive engagement in the cylindrical chamber 22 of the shank part 11 and also fixed in the shank part 12 by the threaded sleeve 13. The cartridge 30 and also the piston 31 preferably consist of a suitable plastic material and, when the entire polishing agent has been pressed out, can be easily exchanged by merely unscrewing the threaded sleeve 13 and pulling the cartridge 30 out of the shank part 11.

In the exemplary embodiments as shown, the polishing head 16 preferably consists of a body made of elastomer hardened e.g. by fiber cores and made of a rubber of predetermined hardness, for example. The surface of the polishing head 16 can be roughened and/or have recesses in the form of slits, notches or countersinks which have a certain depot function for the polishing agent.

The polishing head 16 can also contain several outer layers, a design of which is shown in FIG. 2 a. The body of this polishing head 16 also consists of an elastomer optionally reinforced by short fibers, on the upper side of which a layer 29 a of a fiber material, e.g. a felt, and on top of this layer 29 a a fabric 29 b made of high-strength synthetic fibers are permanently fixed. This embodiment of the polishing head 16 is extremely wear-resistant, yields desired removal rates depending on the mesh width of the fabric 29 b and has an excellent temperature resistance. The two layers 29 a and 29 b are preferably vulcanized into the rubber-like elastomer material. Passages 28 for the polishing agent are also provided in the form of fine bores or capillaries in this polishing head 16, via which the polishing agent is passed from the conical or funnel-shaped pressure chamber 27 to the outer side of the polishing head.

In the exemplary embodiment shown in FIG. 3, the tool shank 15 of the polishing tool 10 corresponds to the outer shank part 11 shown in FIG. 2, i.e. the tool shank 15 is made as one piece. The tool holder SK40 is a steep taper holder, at the integrated end portion 35 of which a hollow-cylindrical extension 36 is formed. A thickened end flange of the shank part 11 meshes with this extension 36 and is fixed by means of a cap nut 13. The functioning of this exemplary embodiment corresponds to that of the embodiment according to FIG. 2. A cartridge 30 having a piston 31 moving longitudinally therein can be used and can be replaced after unscrewing the cap nut 13. The cartridge 30 can also be omitted and in this case the polishing agent filling is inserted directly in the open chamber 22 of the disassembled tool shank and the displacement piston is positioned.

FIG. 4 shows the polishing tool 10 installed in the tool holder 4 (WZ_HSK63). The machine-side inner shank part 12 is positioned in the central recess of the workpiece holder 4 and is fixed by the bolt 20 engaging in the groove 19. The outer shank part 11 corresponds to those of the exemplary embodiments of FIGS. 1 to 3.

The invention is not limited to the exemplary embodiments as shown. For example, the polishing head 16 can be cylindrical with a rounded marginal edge, conical or cone-shaped or also be disk-like instead of having the spherical outer shape as shown. Furthermore, a porous sponge-like material of sufficient strength can be chosen for the polishing head 16 and allows for a continuous passage of the flowable polishing agent selected for this purpose.

The invention creates a processing system by means of which complex cutting faces, also of complex contours, can be milled, ground and polished up to high-gloss automatically and without manual interference and with one clamping, irrespective of the respective shape of the contours. To this end, the polishing tools formed according to the invention are used in the CNC-controlled five-axis milling machine in the same way as the conventional cutting tools, i.e. are held available in a corresponding number in the respective tool magazine and are exchangeably fitted into the work spindle. Since the work spindles of the milling machines and machining centers used in the mold design can be operated in several axes by corresponding swiveling movements of the spindle head or the workpiece table, conditions equal or similar to those for milling result for polishing as well. Thus, there is a further possible use for the highly complex program-controlled machine tools and machining centers, in particularly during the night shifts, by means of which the workpieces machined in several milling steps beforehand can be ground and finally also polished. In particular the extremely time-consuming polishing operations save considerable time and cost. In the polishing method using the apparatus according to the invention, a polishing tool exchangeably fitted into the work spindle automatically by means of the machine control and of the tool changer is rotationally driven and moved continuously or cyclically in several axes. The settable speeds are usually several 1000 to several 10000 rpm. The polishing tool is moved over the workpiece surface to be processed by controlled three-dimensional movements of the work spindle and/or the workpiece including the possible swiveling movements. The respectively optimized orientation of the polishing tool or the tool shank is given by the machine control so as to ensure that the most effective areas of the polishing head are effective on the workpiece surface. What is essential for the polishing operation and also for the smoothness achieved is that the polishing head is moved over the workpiece surface with a virtually constant contact pressure that is optimal according to preselected parameters. The movements are predetermined in respect of speed, trajectory and direction of the machine control, wherein the polishing movements over the respective surface are repeated until the desired polishing degree has been reached. The constant slight contact pressure of the polishing head is achieved by working with what is called an “undersize”, i.e. the polishing head dimensions stored in the machine control consider an intended head material deformation which corresponds to a certain pressure value.

The pressure which is used for forcing the polishing agent out of the cylinder chamber 32 corresponds to the pressure in the machine-side chamber 33 that is supplied via the channel 18 from the work spindle 1. During the polishing operation, the working fluids of the milling machine e.g. the coolant and lubricant, the outer compressed air, etc., are shut off and only the blow air supplied to the work spindle on the inside is effective. This blow air is controlled by a pressure control valve 38 which is shown in FIG. 5 and is connected to the compressed air supply line 39 to the work spindle 1. 

What is claimed is: 1-10. (canceled)
 11. An apparatus for polishing workpiece surfaces, the apparatus comprising: a tool holder configured to be clamped into a spindle of a program-controlled machine tool; a polishing tool fixed in the tool holder and comprised of a tool shank at one end and a polishing head arranged at the five end thereof; means for supplying a polishing agent to the polishing head; a pressurizable chamber in the tool shank which is selectively at least partially filled with the polishing agent the pressurizable chamber being connected to the polishing head; and at least one passage in the polishing head for the polishing agent to be forced out of the chamber.
 12. The apparatus according to claim 11 wherein the pressurizable chamber in the tool shank is connected to a pressure medium supply of the milling machine via a channel, the pressurizable chamber containing a displacement piston on one side of which a pressure medium impinges and which acts on the polishing agent in the chamber.
 13. The apparatus according to claim 1 wherein the polishing tool is configured to be transferred from a machine tool magazine to the work spindle of the program-controlled milling machine by means of a tool changer.
 14. The apparatus according to claim 11, wherein the tool shank is made of one piece and is detachably connected to the tool holder for access to the pressurizable chamber.
 15. The apparatus according to claim 12, wherein the tool shank is made of one piece and is detachably connected to the tool holder for access to the pressurizable chamber.
 16. The apparatus according to claim 11, wherein the tool shank comprises: an inner shank part configured to be connected in the tool holder; and an outer shank part containing the pressurizable chamber, the polishing head being attached at the outer end of the outer shank part; wherein the two shank parts are detachably connected to one another.
 17. The apparatus according to claim 11, and further comprising an exchangeable cartridge removably arranged in the pressurizable chamber.
 18. The apparatus according to claim 11, wherein the polishing head comprises at least partially or an elastomer and a fiber-composite material.
 19. The apparatus according to claim 17, wherein the polishing head comprises at least partially of an elastomer and a fiber-composite material.
 20. The apparatus according to claim 11, wherein the polishing head comprises a material selected from the group consisting of felt, sponge, and steel brush, through which the polishing agent can permeate.
 21. The apparatus according to claim 11, wherein the polishing head is formed with bores for the passage of the polishing agent.
 22. The apparatus according to claim 18, wherein the polishing head comprises a core element made of fiber-reinforced elastomer which is coated with at least one layer of an insulating fiber material and of a high-strength synthetic fabric.
 23. The apparatus according to claim 20, wherein the polishing head comprises a core element made of fiber-reinforced elastomer which is coated with at least one layer of an insulating fiber material and of a high-strength synthetic fabric.
 24. The apparatus according to claim 12, wherein the pressure medium introduced into the pressurizable chamber is a cooling lubricant of the machine tool. 